I've had only one occasion where i knew it was deja vu, and it was a huge event, but i have had conversations or even moments where i KNOW ive done it before, be it driving by a street ive never been to, but feel like i have, or say something to someone that feels like ive said exactly before under the same context.. it really is an amazing thing, people say the brain while asleep can calculate amazing things at amazing speeds, and hence reach solutions we would consciously never imagine..